This application claims the benefit of German Patent Application No. 198 32 871.0 filed on Jul. 22, 1998, the content of which is expressly incorporated by reference herein.
1. Field of the Invention
This invention relates to methods and devices for slitting a material web, and more specifically to a method and device for slitting a material web traveling in the run direction in which the absolute position of a cutting edge of at least one knife unit, on a carrier in a machine frame, is established by combining measurements obtained by two measurement transducers.
2. Discussion of Background Information
Paper webs are frequently produced in widths that are too large for the subsequent user. Modem papermaking machines produce paper webs in widths of up to approximately 10 m. Users, such as printing businesses, currently use paper webs up to a maximum of approximately 3.8 m. In most cases, the desired width is even smaller, namely in the range of approximately 0.8 to 2 m.
Therefore, it is necessary to divide the paper web into several web sections before reeling it onto winding rolls. This slitting is done at each slitting line with a knife unit that usually operates in a xe2x80x9cscissor-likexe2x80x9d manner. The knife unit may include a circular top knife on one side of the paper web and a likewise circular bottom knife on the other side of the paper web. At least one of these knives is driven. The plane of contact between the top knife and the bottom knife forms the cutting edge. The cutting edge usually coincides with one end face of the bottom knife.
The web section width desired by the customer is usually specified rather precisely. The permissible variations in this regard lie in the region of approximately xc2x10.25 mm. In order to achieve this precision, it must be possible to position the cutting edges of the knife unit with corresponding precision. Once the knife unit has been brought into the desired position, it is normally necessary to measure once again to determine whether the cutting edge has also reached the desired position. For example, a steel tape measure that is stretched parallel to the direction of motion of the carrier from a precisely defined reference position on the machine frame with specified tension may be used for this purpose. The positions of the individual cutting edges may then be read from this tape measure. If these positions are then entered into a stored-program control unit, other positions may subsequently be attained, for example, by changing the cutting plane. This process is also referred to as manual calibration. This type of manual calibration is relatively laborious and time-consuming.
DE 34 07 258 A1 discloses moving a measurement transducer across the working width after the positioning of the carrier and thus the cutting edges. The measurement transducer measures the positions of the cutting edges relative to a zero point fixed with respect to the machine. However, the individual cutting edge positions can be measured in this manner only one at a time. A continuous measurement is not possible. For this reason, the determination of all positions takes a relatively long time, and indeed takes more time the longer the measurement distance is. The determination of the cutting edge positions is relative. Further, the values of the positions are not available immediately after the device starts up.
DE 34 17 042 C2 discloses a similar process in which, on the one hand, the position of the carrier in the machine frame is measured, but, on the other hand, the position of the knife edge on the respective carrier is also measured. To accomplish this, the individual carriers are moved sequentially past sensors that are fixed to the machine frame, where the time between the passage of a marking on the carrier and the passage of the cutting edge permits a determination about the distance from the cutting edge to this marking. This procedure is advantageous in that information about the position of the carrier in the machine frame is available on an ongoing basis during operation. However, the absolute position of the cutting edge is still subject to error. This results from the fact that, on the one hand, the position of the cutting edge can only be measured in a relative manner, and, on the other hand, errors arising during operation, for example, as a result of wear, are not detected.
The knives of a knife unit must normally be resharpened from time to time. Consequently, recalibration is required after each resharpening. In addition, wear phenomena occur during operation which are the same order of magnitude as the tolerance range.
Accordingly, the present invention is directed to a method and device for slitting a material web that substantially obviates one or more of the problems arising from the limitations and disadvantages of the related art.
It is an object of the present invention to provide a method and device for slitting a material web that improves the determination of the position of the cutting edge of a knife unit.
It a further object of the present invention to provide a method and device for slitting a material web that continuously monitors the position of the cutting edge of a knife unit.
Another object of the present invention is to provide a method and device for slitting a material web that outputs an error message if the monitored position of the cutting edge of a knife unit falls below a predetermined minimum, or is above a predetermined maximum.
Accordingly, one aspect of the present invention is directed to a method for slitting a material web traveling in the run direction. A knife unit on a carrier in a machine frame is moved transversely to the run direction. The position of a cutting edge of the knife unit on the carrier is measured. The position of the carrier in the machine frame is measured. An absolute position of the cutting edge in the machine frame is established by combining the measured position of the cutting edge on the carrier and the position of the carrier in the machine frame.
According to another aspect of the present invention, the position of the cutting edge on the carrier is measured by measuring a distance between the cutting edge and a first reference point that is fixed with respect to the carrier.
According to yet another aspect of the present invention, the invention includes monitoring to determine whether the distance between the cutting edge and the first reference point exceeds a predetermined minimum dimension, and outputting an error message if the distance between the cutting edge and the first reference point exceeds the predetermined minimum dimension.
In a further aspect of the present invention, the invention includes monitoring to determine whether the distance between the cutting edge and the first reference point falls below a predetermined maximum dimension, and outputting an error message if the distance between the cutting edge and the first reference point falls below the predetermined maximum dimension.
According to another aspect of the present invention, both the position of the cutting edge on the carrier and the position of the carrier in the machine frame are continuously measured.
According to yet another aspect of the present invention, the invention includes resting a mating knife against the cutting edge. The mating knife is spring biased and located on a bottom side of the material web. The cutting edge and the mating knife operate in a scissor-like manner to create a cutting line in the material web defined by the position of the cutting edge.
According to a further aspect of the present invention, the position of the cutting edge on the carrier and/or the position of the carrier in the machine frame are measured optically.
According to another aspect of the present invention, the position of the cutting edge on the carrier and/or the position of the carrier in the machine frame are measured acoustically.
According to yet another aspect of the present invention, the position of the cutting edge on the carrier and/or the position of the carrier in the machine frame are measured magnetically.
According to a further aspect of the present invention, the position of the cutting edge on the carrier and/or the position of the carrier in the machine frame are measured electromagnetically.
According to another aspect of the present invention, the position of the cutting edge on the carrier and/or the position of the carrier in the machine frame are measured capacitively.
A further aspect of the present invention is directed to a device for slitting a material web traveling in the run direction including at least one knife unit having a cutting edge. The at least one knife unit is on a carrier movable transversely to the run direction in a machine frame. A measurement device exists to measure the position of the cutting edge. The measurement device includes a first measurement transducer and a second measurement transducer. The first measurement transducer is arranged on the carrier and measures the distance of the cutting edge to a first reference point that is fixed with respect to the carrier. The second measurement transducer measures the distance to a second reference point that is fixed with respect to the carrier from a zero point. The zero point is fixed in a machine frame.
According to another aspect of the present invention, the second measurement transducer includes a stationary active part and a movable passive part.
According to yet another aspect of the present invention, the active part is a linear measurement scale.
In a further aspect of the present invention, the first reference point and the second reference point coincide.
According to another aspect of the present invention, a comparator is connected to the first measurement transducer. The comparator outputs an error message if the distance of the cutting edge to the first reference point exceeds a predetermined value.
According to yet another aspect of the present invention, a comparator is connected to the first measurement transducer. The comparator outputs an error message if the distance of the cutting edge to the first reference point drops below a predetermined value.
A further aspect of the present invention is directed to a device for slitting a material web traveling in the run direction that includes: a carrier in a machine frame where the carrier is movable transversely to the run direction; at least one knife unit having a cutting edge where the at least one knife unit is attached to the carrier; a first measurement transducer arranged on the carrier and that measures the distance of the cutting edge to a first reference point that is fixed with respect to the carrier; and a second measurement transducer that measures the distance to a second reference point that is fixed with respect to the carrier from a zero point where the zero point is fixed in a machine frame, and wherein an absolute position of the cutting edge in the machine frame is established by combining the measured distance of the cutting edge to the first reference point and the measured distance of the second reference point to the zero point in the machine frame.
According to another aspect of the present invention, the carrier is supported on rollers that are movable along rails.
According to yet another aspect of the present invention, the at least one knife unit includes a circular knife driven by a motor.
In a further aspect of the present invention, the invention includes a mating knife located on a bottom side of the material web where the mating knife is under a spring force and rests against an end face of the circular knife. The circular knife and the mating knife operate in a scissor-like manner to create a cutting line in the material web defined by the position of the cutting edge.
According to another aspect of the present invention, the first measurement transducer and/or the second measurement transducer operate in a non-contacting manner.
According to yet another aspect of the present invention, the non-contacting manner is optical.
According to a further aspect of the present invention, the non-contacting manner is acoustical.
According to another aspect of the present invention, the non-contacting manner is magnetic.
According to yet another aspect of the present invention, the non-contacting manner is electromagnetic.
According to a further aspect of the present invention, the non-contacting manner is capacitive.
According to yet another aspect of the present invention, the first reference point and the second reference point coincide.
In a further aspect of the present invention, a comparator is connected to the first measurement transducer where the comparator outputs an error message if the distance of the cutting edge to the first reference point exceeds a predetermined value.
According to another aspect of the present invention, a comparator is connected to the first measurement transducer where the comparator outputs an error message if the distance of the cutting edge to the first reference point drops below a predetermined value.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawings.